fix(dialog): don't clobber md-dialog id

Author: jelbourn

src/components/dialog/dialog.js

@@ -896,7 +896,8 @@ function MdDialogProvider($$interimElementProvider) {
 
       var role = (options.$type === 'alert') ? 'alertdialog' : 'dialog';
       var dialogContent = element.find('md-dialog-content');
-      var dialogContentId = 'dialogContent_' + (element.attr('id') || $mdUtil.nextUid());
+      var existingDialogId = element.attr('id');
+      var dialogContentId = 'dialogContent_' + (existingDialogId || $mdUtil.nextUid());
 
       element.attr({
         'role': role,
@@ -905,6 +906,10 @@ function MdDialogProvider($$interimElementProvider) {
 
       if (dialogContent.length === 0) {
         dialogContent = element;
+        // If the dialog element already had an ID, don't clobber it.
+        if (existingDialogId) {
+          dialogContentId = existingDialogId;
+        }
       }
 
       dialogContent.attr('id', dialogContentId);

src/components/dialog/dialog.spec.js

@@ -168,6 +168,27 @@ describe('$mdDialog', function() {
       expect(content.id).toBe('dialogContent_' + dialog[0].id);
     }));
 
+    it('should not clobber the id from `md-dialog` when there is no content', inject(function ($mdDialog, $rootScope, $document) {
+      jasmine.mockElementFocus(this);
+
+      var parent = angular.element('<div>');
+
+      $mdDialog.show(
+        $mdDialog.alert({
+          template: '<md-dialog id="demoid">' +
+          '<p>Muppets are the best</p>' +
+          '</md-dialog>',
+          parent: parent
+        })
+      );
+
+      runAnimation();
+
+      var dialog = parent.find('md-dialog');
+
+      expect(dialog[0].id).toBe('demoid');
+    }));
+
     it('should apply a prefixed id for `md-dialog-content`', inject(function ($mdDialog, $rootScope, $document) {
       jasmine.mockElementFocus(this);